Osteology of Upper Limb: Clavicle

Overview

• The clavicle is the only long bone in the human body that is horizontal and subcutaneous.
• Commonly referred to as the collarbone or beauty bone.
• First bone to begin ossifying, starting in the fifth and sixth week of intrauterine life.
• Has two primary centers of ossification, which is exceptional among long bones.
• Controversial regarding the presence of a medullary cavity.

Anatomy of the Clavicle

General Characteristics

• Location: Superior view of the right clavicle.
• Shape: Medial end is round/quadrangular; lateral end is flat.
• Articulations:
  • Medial end articulates with the sternum to form the sternoclavicular joint.
  • Lateral end articulates with the acromion process to form the acromioclavicular joint.
• Surfaces:
  • Superior surface is smooth.
  • Inferior surface has rough impressions.
    • Subclavian groove: Lodges the subclavian vessels (artery and vein).
    • Conoid tubercle and trapezoid ridges: Located laterally on the inferior surface.

Shaft Characteristics

• Shape: Medial two-thirds of the clavicle is convex anteriorly.
• Muscle Attachments:
  • Medial Two-Thirds Anterior Surface:
    • Attachment for the clavicular head of pectoralis major.
  • Medial Two-Thirds Superior Surface:
    • Origin for sternocleidomastoid muscle.
  • Inferior Surface:
    • Attachment for costoclavicular ligament (medially).
    • Insertion for subclavius muscle (middle part).
  • Lateral One-Third:
    • Anterior border: Origin for anterior fibers of deltoid.
    • Posterior border: Attachment for upper fibers of trapezius.
    • Inferior surface: Trapezoid ridge and conoid tubercle provide attachment for the coracoclavicular ligament.

Ossification of the Clavicle

• Primary Centers:
  • Appear in medial and lateral parts of the shaft during fifth to sixth weeks of intrauterine life.
  • Fuse by the 45th day of intrauterine life.
• Secondary Centers:
  • For the sternal end (medial): Appears at 19-20 years, fuses by 25 years.
  • For the acromial end (lateral): Appears occasionally at 20 years; fuses immediately.

Clinical Aspects

• Fracture: Commonly occurs at the junction of the middle two-thirds and lateral one-third.
  • Displacement:
    • Proximal fragment: Upward due to pull of sternocleidomastoid muscle.
    • Distal fragment: Downward due to pull of deltoid muscle and gravity.

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